Adding disk space to an account

I need to create something that will allow me to add disk space plans to specific accounts as needed. For example, client accesses his account via WHMCS, adds a 100 or 200mb disk space plan to his account then that info gets passed to the WHM and the disk space gets added.

Problem is, I have no clue where to start. I'm not a programmer and can't seem to find anyone who can create this (whmcs folks say cpanel/whm doesn't allow for this) but according to some recent docs I've found:EditQuota < AllDocumentation/AutomationIntegration < TWiki
it would seem that this should now be possible to do.

Can anyone tell me if this would now be possible and perhaps give me some guidance on where I should start to tackle this on the cpanel/whm side of things?